Interference in cellular networks is becoming a limiting factor with the rapid increase of the number of users of mobile communications, as well as of the data-rates required by more demanding applications such as mobile internet and streaming services. This has generated a demand for new and efficient ways of improving the interference situation.
Interference from adjacent sectors belonging to the same base station site, i.e., intra-site interference, and from cells belonging to other sites, i.e., inter-site interference, may in many cases reduce the bit-rate in a cellular network. This is particularly valid at sector borders and cell borders when the same frequency bands are used across the whole network (frequency reuse one).
Existing solutions for interference mitigation include higher order sectorization, antenna radiation lobe tilt, underlay/overlay, fractional reuse, and cooperative multicast transmission, i.e., various means of either static or dynamic interference coordination.
Higher-order sectorization implies more cells and an increased number of neighboring cells. This gives rise to more handovers, narrower handover regions with corresponding requirements on rapid cell reallocation, and increased control signaling, and also a general increase in the overall interference level due to the radiation, via the side lobes, from the additional antennas. Higher-order sectorization may therefore lead to performance degradation, lower bit-rates, along sector borders due to a poorer interference situation.
Antenna radiation lobe tilt is useful for inter-site interference management, but does not improve the interference situation along cell borders, neither at borders between cells belonging to the same site, i.e., sectors in a traditional sectorized system, nor on borders between cells belonging to different sites.
Underlay/overlay cells can enable a tight frequency reuse close to the site than at the cell border towards other sites. However, since the power is reduced equally for all underlay cells it does not improve the interference situation at sector borders.
Fractional reuse and coordinated scheduling on site of users in adjacent sectors can be used to improve the interference situation. However, the frequency used by a user terminal near the sector border is then blocked in the whole neighboring sector, thus reducing spectral efficiency.
Cooperative multicast transmission can improve the quality at a sector border significantly, but at the cost of frequencies being explicitly allocated in two sectors, thus reducing spectral efficiency.
There is thus a need to reduce interference from adjacent sectors without the drawbacks of the previously known methods according to the above.